Some addresses exist to receive post for people and companies who are not there. A mail-forwarding branch rents boxes to anyone. A company-formation agent lets thousands of companies name its office as their registered address. A building that carries a crowd of registered companies is, whatever its sign says, one of the two. Spaw has always answered all three with one flag, is_mail_drop, and since 16 September 2026 it says which of the three it found, because the three mean different things about the person in front of you.
Three sources, one flag
mail_drop_source takes one of three values, tried in that order:
operator_list means the address is on the published branch list of a mailbox operator — The UPS Store and PostNet in the United States, and the operators added since. Anyone can rent a box there, and a customer who writes one as a home address is writing a place where nobody lives.
registered_agent means the address is on the bundled list of the offices registered-agent and formation services stand at: nine American registered agents, five of them in Delaware, where a large share of American companies are registered, and eight London formation and registered-office services, the busiest of whose addresses, 71-75 Shelton Street, is the registered office of 86,789 companies in the 1 September 2026 Companies House snapshot as the lookup counts them. On 16 September 2026 the list named seventeen operators. mail_drop_provider carries the agent's name, because that is a fact about the agent's own business.
company_cluster means neither list knows the address, but an open company register lists more companies at it than the published threshold. It is a heuristic about a building, and companies_registered carries the count so the evidence sits beside the flag.
All three carry the same mail_drop weight of +50, because the question the flag answers — does somebody live here? — has the same answer for all three: no.
Why the distinction matters anyway
The weight is the same; the decision you make with it is not.
A business onboarding check that meets a registered-agent address has met the most ordinary thing in company formation. In Delaware the agent's office is the registered office of a great many companies, by design, and a company that names one has complied with the law rather than evaded it. The right reading is "the registered office is an agent's; ask for the trading address", and registered_agent is what lets a rule say exactly that instead of "mail drop, decline".
A residence check that meets the same address has met something else entirely. Nobody lives at 251 Little Falls Drive, and a proof-of-address form that names it is naming a place that receives the company's legal post. That is what the +50 is for.
A company_cluster sits between the two. The building might be a formation agent the list does not know, a serviced office, a large landlord's registered address, or a genuinely busy commercial building; the count tells you how busy, and the threshold that turned the count into a flag is published in the documentation so the arithmetic can be checked.
What the answer never says
It never says a company is suspicious for being registered at an agent's address, and the documentation is written so nobody can quote it that way. It never names a person, and it carries no register of who is registered where: companies_registered is a count, and the agent list holds the agents' own addresses and nothing about their clients. And it never treats a private mailbox — a PMB number at a real street address — as the same thing as an agent's office: that is address_type: private_mailbox with its own weight of +60, decided from the way the postal service requires such an address to be written, not from any list.
Where the list comes from
The agent list ships with the product as a versioned data file, and every entry is an address the agent publishes as its own, or that public filings naming the agent's service carry, and the file says which for each. In the 16 September 2026 version, four of the seventeen were checked on the agent's own site — the registered-office address on a formation agent's order page, the "our address" line on a registered agent's contact page — two American and two British. The other thirteen were checked against the public record instead: three against the Delaware Division of Corporations' registered-agent listing, four against Secretary of State filings in Wyoming, Washington, Nevada and Texas, and six against Companies House filings that name the service. A filing is read for the service's own address and nothing else: nothing in the list comes from a review site or a customer's report, and nothing in it names a client. The file's version appears in the answer's sources as registered-agents whenever it decided the answer, so a change to the list is visible in the response that used it.
Each entry is keyed the way a national register is: the street name folded to its comparison form, the postcode or town, and the house number with both ends of a range tried, so "71-75 Shelton Street", "71 Shelton St" and "75 SHELTON STREET" all find the same agent. An agent's address the list does not yet hold falls through to the company register, where the cluster usually catches it anyway; the count is published beside the flag either way.
Reading it in a workflow
For a residence claim, treat every mail_drop_source alike: the address cannot prove where somebody lives, and the score already says so. For a company's registered office, treat registered_agent as normal, operator_list as a question ("why is the registered office a rented box?") and company_cluster as a count to read. For a trading address, ask for one that answers none of the three. The flag is a fact about a place; which of your decisions it should change is yours to write.